Touch sensor systems, such as touchscreens or touch monitors, can act as input devices for interactive computer systems used for various applications, for example, information kiosks, order entry systems, video displays, etc. Such systems may be integrated into a computing device, thus providing interactive touch capable computing devices, including computers, electronic book readers, mobile communications devices, trackpads, and touch sensitive surfaces more generally.
Generally, touch sensor systems enable the determination of a position on the surface of a substrate via a user's touch of the surface. The touch substrate is typically made of some form of glass which overlies a computer or computing device display, like a liquid crystal display (LCD), a plasma display, etc. The touch sensor system is operatively connected to the device display so that it also enables the determination of a position on the device display and, moreover, of the appropriate control action of a user interface shown on the display. Alternatively, the touch substrate may be opaque such as for trackpad applications where the display may be located away from the touch sensor.
Touch sensor systems may be implemented using different technologies. Acoustic touch sensors, such as ultrasonic touch sensors using surface acoustic waves, are currently one of the major touch sensor technologies and many types of acoustic touch sensors now exist. For example, a “non-Adler-type” acoustic touch sensor uses a number of transducers per coordinate axis of the sensor substrate to spatially spread a transmitted surface acoustic wave signal and determine the touch surface coordinates by analyzing spatial aspects of the wave perturbation from a touch of the touch surface. An “Adler-type” acoustic touch sensor uses only two transducers per coordinate axis to spatially spread a transmitted surface acoustic wave signal and determine the touch surface coordinates by analyzing temporal aspects of a wave perturbation from a touch. For each axis of the substrate of the “Adler-type” sensor, one transducer at a respective peripheral surface generates surface acoustic wave pulses that propagate through the substrate across a perpendicular peripheral surface along which a first reflective grating or array is disposed. The first reflective array is adapted to reflect portions of a surface acoustic wave perpendicularly across the substrate along plural parallel paths to a second reflective array disposed on the opposite peripheral surface. The second reflective array is adapted to reflect the surface acoustic wave along the peripheral surface to a second transducer at a respective perpendicular peripheral surface where the wave is received for processing. The reflective arrays associated with the X axis are perpendicular to the reflective arrays associated with the Y axis so as to provide a grid pattern to enable two-dimensional coordinates of a touch on the substrate to be determined. Touching the substrate surface at a point causes a loss of energy by the surface acoustic waves passing through the point of touch. This is manifested as an attenuation of the surface acoustic waves. Detection circuitry associated with each receiving transducer detects the attenuation as a perturbation in the surface acoustic wave signal and performs a time delay analysis of the data to determine the surface coordinates of a touch on the substrate. This type of sensor is shown in FIG. 1 and described in more detail below.
Historically, the operative elements of an acoustic touch sensor, i.e., the transducers and reflective arrays, which are on the front surface of the substrate, have been covered and hidden from view by a protective bezel provided by the housing of the touch sensor or the device integrating the sensor. Current trends eliminate the bezel in favor of flush surroundings of touch area, even for larger-sized devices. Moreover, possible future applications of touch technology, such as turning passive objects like glass table tops into touch input devices and endowing robots with a sense of touch in their exterior shells, further motivate moving the operative elements from the exterior touch sensing surface of the touch substrate to the protected and hidden interior surfaces of the substrate. Acoustic touch sensors may utilize a rounded-substrate-edge approach to obtain such a zero-bezel or bezel-less design. This type of sensor is also described in more detail below.
Recently, acoustic touch sensors having multi-touch capability have been introduced into the commercial marketplace. Multi-touch capability is generally defined as the ability of a touch sensor to sense or recognize two or more (i.e., multiple) simultaneous touch points. Multiple simultaneous touch points include, for example, pinching gestures, parallel line swipes, and pivoting movements. To date, acoustic touch sensors, such as the IntelliTouch™ Plus touch sensors by Tyco Electronics Corporation have been able to deliver dual touch performance. Certain other touch technologies are even providing higher levels of multi-touch performance. The competition between the different technologies and the increase of system applications using multi-touch is now increasing the expectation and demand by users and designers for good touch performance not only for dual touches but also for three or more simultaneous touches.
A difficulty for acoustic touch sensors to support two or more simultaneous touches rests on such sensors not being able to acquire sufficient, clear coordinate information to match respective X coordinates with the respective corresponding Y coordinates of the multiple touches. The difficulties increase as the number of simultaneous touches increases.